The halogen-substituted-benzenesulfonanilides of the above generic formula generically are known compounds. Their preparation is taught in French Pat. No. 7,137,123. The disclosed compounds are stated as possessing antibacterial and antifungal activity. Further, certain O-hydroxyhalo-benzenesulfonanilides have been prepared by Schraufstatter et al. (z. Naturtorschung, 16b, 95, 1961) and disclosed as having activity as molluscicides. Earlier work by Foetchius et al (J. Lab. Clin. Med., 32: 1361, 1947) indicates that the introduction of a hydroxyl group into a phenyl ring of a benzenesulfonanilide system results in a decrease of the activity possessed by the compounds. It has now been found in accordance with the present invention that a limited group of O-hydroxy- or O-lower alkanoyloxy- halogen-substituted-benzenesulfonanilides surprisingly possess marked anthelmintic activity in the treatment of liver fluke infections.